This invention relates to topical anesthesia, and more particularly to apparatus and method for inducing anesthesia of a body surface by the rapid cooling action of ethyl chloride.
Ethyl chloride, also known as chloroethane, has a boiling point of 12.27.degree. C. Wohen applied as a liquid to skin having a temperature of about 37.degree. C., it boils off rapidly. The skin temperature is rapidly reduced as heat from the skin is transferred to the liquid and converted to heat of vaporization as the liquid is converted to gas. The skin becomes so cold that it is anesthetized.
This phenomenon has been employed for topical anesthesia for at least a century. Because of the high vapor pressure of the liquid at room temperature, it is stored in a pressure resistant container. The container is fitted with a spring loaded valve. When the valve is depressed a jet or straight stream of the liquid is emitted. This stream is directed to the skin surface to be anesthetized. When the stream hits the surface, it spreads out on the surface while it boils. The point of impingement of the stream is flushed with fresh liquid while the perimeter of the fluid pool is boiling. Consequently, the surface wet by the liquid is not uniformly cooled. The user may move the stream around on the skin surface to try to provide more uniform or larger cooling action. While this apparatus and method have been in use for at least about a century, a means of more uniform cooling and better adjustment of the area cooled would be helpful.